Super Mario; the one that had the 10 Koopas (Bowser+9 brothers), and Yoshis all over the place.
Dune 2000- my 1st foray into the world of RTS, I love this game.
Battlefield 1942-Vietnam, 2142- I haven't played BF2; if it weren't for Battlefield Vietnam, I would never have become a gamer. Thank you DICE.
Sins/Entrenchment- personally, I think this one's a no-brainer. I LOVE this game, and it's much easier to mod than the BF-series.
Vega Strike- an awesome free-form open-source space sim.
Quake II- I found this game ludicrously easy, but AWESOMELY FUN. Spamming a Super Shotgun at cybernetic aliens was the bomb.
Tiberium Sun- I haven't actually played this game, but I did play the demo. Now I want the game.
Tiberium Wars- once again, only played the demo. I liked the Skirmish mode, the Campaign was a bit too easy (even on hard); just build a bunch of Mammoth tanks and role through an enemy base.